A conventional practice is to impregnate one or more sample drops of biological material to be examined into a sheet of filter paper, dry the sheet of filter paper impregnated with the biological material, and then send the sheet of filter paper to a laboratory for examination. The biological material to be examined can be, for example, blood of a newborn baby. In the laboratory, one or more sample disks containing the biological material to be examined are cut or punched out from the sheet of filter paper and then the one or more sample disks that have been cut or punched are subjected to analysis. It has, however, turned out that properties of the filter paper may vary between filter papers. In some cases, these property variations may result in variation between measurement results obtained from sheets of filter paper impregnated with same biological material. FIG. 1 shows a histogram of results measured in an example case in which blood was impregnated into seven different sheets of filter paper from different filter paper batches. The analyte was measured by eluting the blood from the sample disk punched out from the filter paper impregnated with blood and by assaying the analyte. The results were obtained by measuring fluorescence. The vertical axis of the histogram shown in FIG. 1 is the count number obtained with the photo detector. The count number is inversely proportional to the activity of analyte. In this example case, the analyte that is measured is biotinidase which is an enzyme that catalyses the cleavage of biotin, vitamin H, from small biotinylated peptides and biocytin, thus, recycling the vitamin. The reaction is hydrolytic, in which the substrate, i.e. the molecules at the beginning of the reaction, is converted to the products of the reaction. For example, biocytin can be converted to biotin and lysine. Biotinidase can also catalyze the cleavage of synthetic substrates that release a fluorescent dye, such as biotin-6-aminoquinoline, for screening of newborns for biotinidase deficiency. Enzyme activity is defined as the moles of substrate converted per unit time. Enzyme activity is a measure of the quantity of active enzyme present and is hence dependent on conditions, which should be specified. The SI unit is the katal, 1 katal=1 mol s−1. A more practical and commonly used value is enzyme unit, 1 (U)=1 μmol min−1. 1 U corresponds to 16.67 nanokatals. As can be seen from FIG. 1, there is, in this exemplifying case, relatively strong variation between results obtained with the different sheets S1-S7 of filter paper.
An inconvenience related to the above described phenomenon is that it may cause additional work and additional requirements to personnel collecting the samples of biological material, to personnel performing the measurements in laboratories, and also to specialists interpreting the analysis results.